1. Field of the Invention
The present invention relates to the preparation of polymers and copolymers, essentially of vinyl type, which are insoluble in their monomeric or comonomeric compositions, and, more especially, to the preparation of such polymers by suspended emulsion polymerization.
By the phrase "suspended emulsion polymerization" is intended the polymerization of at least one monomer in the presence of an initiating system, at least one of the constituents of which is water-soluble, and wherein said initiating system comprises a finely divided aqueous phase dispersed in the monomer(s).
2. Description of the Prior Art
It is known to this art to prepare polymers and copolymers, essentially of vinyl type, which are insoluble in their monomeric or comonomeric starting materials, by polymerization in suspended emulsion entailing dispersing, in a finely divided form and in small quantities, an aqueous solution of at least a part of an initiating system in a monomeric or comonomeric composition of vinyl type, essentially based on vinyl chloride, and then effecting polymerization of such composition. According to this process, the quantity of the aqueous solution does not exceed 10% by weight of the monomeric or comonomeric starting material.
This process has been described in French Patent No. 69,01,008, published under No. 2,029,247, and in its Certificates of Addition thereto, No. 69/37,326, published under No. 2,070,251 and No. 69/37,327, published under No. 2,070,922.
This process enables the production of polymers and copolymers consisting of particles, the mean diameter of which ranges from 0.1 to 2,000 .mu.m and the apparent density of which ranges from 0 10 g/cm.sup.3 to over 0.70 g/cm.sup.3 . Compared with the bulk polymerization processes, this particular process results in the formation of smaller amounts of build-up, as well as the weaker adhesion of such build-up to the walls of the reactors.
In the case of the polymerization of a monomeric or comonomeric composition based on vinyl chloride, at a given polymerization temperature, this process produces polymers and copolymers whose viscosity index, determined according to ISO International Standard 174, is 5 to 10 ml/g higher than that of the polymers and copolymers produced, all other parameters remaining unchanged, according to the other techniques of polymerization and particularly according to the bulk polymerization techniques. It follows that, in order to produce a polymer or copolymer of a given viscosity index, the operation is carried out at a higher polymerization temperature, resulting in a reduced polymerization time.
However, in the case of polymerization of a monomeric or comonomeric composition based on vinyl chloride, such process does not enable the production, at a degree of conversion of the monomeric or comonomeric composition of greater than 10%, of polymers and copolymers consisting of particles having a mean diameter greater than 10 .mu.m and having both an apparent density greater than 0.50 g/cm.sup.3 and a porosity, evaluated by plasticizer uptake at ambient temperature, greater than 15 g of di-2-ethylhexyl phthalate per 100 g of resin.